Olefin conversion process

ABSTRACT

Processes for the production of olefins are disclosed, which may include: contacting a hydrocarbon mixture comprising linear butenes with an isomerization catalyst to form an isomerization product comprising 2-butenes and 1-butenes; contacting the isomerization product with a first metathesis catalyst to form a first metathesis product comprising 2-pentene and propylene, as well as any unreacted C 4  olefins, and byproducts ethylene and 3-hexene; and fractionating the first metathesis product to form a C3− fraction and a C5 fraction comprising 2-pentene. The 2-pentene may then be advantageously used to produce high purity 1-butene, 3-hexene, 1-hexene, propylene, or other desired products.

BACKGROUND OF DISCLOSURE

Field of the Disclosure

Embodiments disclosed herein relate generally to the production of highpurity alpha-olefins, such as C₄ to C₈ olefins, for use in variousdownstream processes, such as use as a co-monomer in the production ofpolyethylenes and polypropylenes, among other end uses. Morespecifically, embodiments disclosed herein relate to the more efficientproduction and purification of alpha-olefins utilizing isomerization andmetathesis.

Background

Processes for producing high purity polymer-grade comonomers includevarious 1-butene comonomer production processes and 1-hexene comonomerproduction processes. These processes utilize metathesis and/ordouble-bond isomerization reactions that occur over specific catalystsusing mixed n-butenes as the feed to produce polymer-grade 1-butene and1-hexene used as comonomers for production of polyethylene. However,these processes are extremely energy intensive as they employdistillation to separate the desired alpha-olefin (1-butene and1-hexene) with high purity from mixtures of their positional isomersthat exhibit very close boiling points (2-butene and 2-hexene, 3-hexene,respectively).

For example, the 1-butene process flow includes a butenessuperfractionator that separates the 1-butene product from 2-butene. The1-hexene process is even more energy intensive as it requires twosuperfractionators: a butenes superfractionator to separate ahigh-purity 1-butene stream used to produce hexenes, and a hexenessuperfractionator to separate the final 1-hexene product from the otherpositional hexene isomers (2-hexene and 3-hexene).

The high operating costs associated with the energy intensivedistillation towers in the processes have significantly hampered thecommercialization efforts for these processes, especially for the1-hexene process that requires two (2) superfractionators.

SUMMARY OF THE DISCLOSURE

In one aspect, embodiments disclosed herein relate to a process for theproduction of olefins. The process may include: contacting a hydrocarbonmixture comprising linear butenes with an isomerization catalyst to forman isomerization product comprising 2-butenes and 1-butenes; contactingthe isomerization product with a first metathesis catalyst to form afirst metathesis product comprising 2-pentene and propylene, as well asany unreacted C₄ olefins, and byproducts ethylene and 3-hexene; andfractionating the first metathesis product to form a C3− fraction and aC5 fraction comprising 2-pentene.

For the production of 1-butene and/or propylene, the process may alsoinclude: (d) contacting ethylene and the C5 fraction with a secondmetathesis catalyst, which may be the same or different than the firstmetathesis catalyst, to convert at least a portion of the 2-pentene andethylene to propylene and 1-butene and form a second metathesis product.The second metathesis product may then be fractionated to form apropylene fraction and a 1-butene fraction. The 1-butene fraction mayhave a purity of at least 98 wt % 1-butene.

For the production of 3-hexene and/or 1-hexene, the process may alsoinclude: contacting the C5 fraction with a second metathesis catalyst,which may be the same or different than the first metathesis catalyst,to convert at least a portion of the 2-pentene to 2-butene and 3-hexeneand form a second metathesis product. The second metatheses product maythen be fractionated to form a 2-butene fraction and a 3-hexenefraction. The 3-hexene fraction may have a purity of at least 98 wt %3-hexene. To produce 1-hexene, the process may also include a step forconverting the 3-hexene fraction via isomerization to 1-hexene.

In another aspect, embodiments disclosed herein relate to a process forthe production of olefins. The process may include: feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the C4-olefin streamwith the isomerization catalyst in the first reaction zone to form anisomerization product comprising 2-butene and 1-butene; contacting theisomerization product with the metathesis catalyst in the secondreaction zone to form a first metathesis product comprising 2-pentene,propylene, and byproducts ethylene and 3-hexene; feeding the firstmetathesis product to a fractionation system; fractionating the firstmetathesis product in the fractionation system to form at least one C3−fraction and a C5 fraction comprising 2-pentene.

In another aspect, embodiments disclosed herein relate to a process forthe production of olefins. The process may include: feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the C4-olefin streamwith the isomerization catalyst in the first reaction zone to form anisomerization product comprising 2-butene and 1-butene; contacting theisomerization product with the metathesis catalyst in the secondreaction zone to form a first metathesis product comprising 2-pentene,propylene, and byproducts ethylene and 3-hexene; feeding the firstmetathesis product to a fractionation system; fractionating the firstmetathesis product in the fractionation system to form at least one C3−fraction and a C5 fraction comprising 2-pentene; feeding ethylene andthe C5 fraction to a metathesis reactor and contacting the 2-pentenewith a second metathesis catalyst, which may be the same or differentthan the first metathesis catalyst, to convert at least a portion of theethylene and 2-pentene to propylene and 1-butene and recovering a secondmetathesis product; fractionating the second metathesis product torecover a propylene fraction and a 1-butene fraction.

In another aspect, embodiments disclosed herein relate to a process forthe production of olefins. The process may include; feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the C4-olefin streamwith the isomerization catalyst in the first reaction zone to form anisomerization product comprising 2-butene and 1-butene; contacting theisomerization product with the metathesis catalyst in the secondreaction zone to form a first metathesis product comprising 2-pentene,propylene, and byproducts ethylene and 3-hexene; feeding the firstmetathesis product to a fractionation system; fractionating the firstmetathesis product in the fractionation system to form at least one C3−fraction and a C5 fraction comprising 2-pentene; feeding the C5 fractionto a metathesis reactor and contacting the 2-pentene with a secondmetathesis catalyst, which may be the same or different than the firstmetathesis catalyst, to convert at least a portion of the 2-pentene to2-butene and 3-hexene and recovering a second metathesis product;fractionating the second metathesis product to recover a 2-butenefraction and a 3-hexene fraction.

In another aspect, embodiments disclosed herein relate to a process forthe production of olefins. The process may include: feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the C4-olefin streamwith the isomerization catalyst in the first reaction zone to form anisomerization product comprising 2-butene and 1-butene; contacting theisomerization product with the metathesis catalyst in the secondreaction zone to form a first metathesis product comprising 2-pentene,propylene, and byproducts ethylene and 3-hexene; feeding the firstmetathesis product to a fractionation system; fractionating the firstmetathesis product in the fractionation system to form an ethylenefraction, a propylene fraction, a C4 fraction and a C5+ fractioncomprising 2-pentene and 3-hexene; feeding ethylene and the C5 fractionto a metathesis reactor and contacting the 2-pentene with a secondmetathesis catalyst, which may be the same or different than the firstmetathesis catalyst, to convert at least a portion of the ethylene and2-pentene to propylene and 1-butene and to convert at least a portion ofthe 3-hexene and ethylene to 1-butene and recovering a second metathesisproduct; feeding the second metathesis product to the fractionationsystem.

In another aspect, embodiments disclosed herein relate to a system forthe production of olefins. The system may include: anisomerization/metathesis reaction system for: contacting a hydrocarbonmixture comprising linear butenes with an isomerization catalyst to forman isomerization product comprising 2-butenes and 1-butenes; andcontacting the isomerization product with a first metathesis catalyst toform a first metathesis product comprising 2-pentene and propylene, aswell as any unreacted C₄ olefins, and byproducts ethylene and 3-hexene;a fractionation system for fractionating the first metathesis product toform a C3− fraction and a C5 fraction comprising 2-pentene.

In another aspect, embodiments disclosed herein relate to a system forthe production of olefins. The system may include: anisomerization/metathesis reactor including an inlet for feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene andincluding a first reaction zone comprising an isomerization catalyst anda second reaction zone comprising a first metathesis catalyst for:contacting the C4-olefin stream with the isomerization catalyst in thefirst reaction zone to form an isomerization product comprising 2-buteneand 1-butene; contacting the isomerization product with the metathesiscatalyst in the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene.The system may also include: a fractionation system for fractionatingthe first metathesis product to form at least one C3− fraction and a C5fraction comprising 2-pentene.

In another aspect, embodiments disclosed herein relate to a system forthe production of olefins. The system may include: anisomerization/metathesis reactor including an inlet for feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene andincluding a first reaction zone comprising an isomerization catalyst anda second reaction zone comprising a first metathesis catalyst for:contacting the C4-olefin stream with the isomerization catalyst in thefirst reaction zone to form an isomerization product comprising 2-buteneand 1-butene; contacting the isomerization product with the metathesiscatalyst in the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene.The system may also include: a fractionation system for fractionatingthe first metathesis product to form at least one C3− fraction and a C5fraction comprising 2-pentene; a metathesis reactor and contactingethylene and the 2-pentene in the C5 fraction with a second metathesiscatalyst, which may be the same or different than the first metathesiscatalyst, to convert at least a portion of the ethylene and 2-pentene topropylene and 1-butene and recovering a second metathesis product; and asecond fractionation system for fractionating the second metathesisproduct to recover a propylene fraction and a 1-butene fraction.

In another aspect, embodiments disclosed herein relate to a system forthe production of olefins. The system may include: anisomerization/metathesis reactor including an inlet for feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene andincluding a first reaction zone comprising an isomerization catalyst anda second reaction zone comprising a first metathesis catalyst for:contacting the C4-olefin stream with the isomerization catalyst in thefirst reaction zone to form an isomerization product comprising 2-buteneand 1-butene; contacting the isomerization product with the metathesiscatalyst in the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene.The system may also include: a first fractionation system forfractionating the first metathesis product to form at least one C3−fraction and a C5 fraction comprising 2-pentene; a metathesis reactorfor contacting the 2-pentene in the C5 fraction with a second metathesiscatalyst, which may be the same or different than the first metathesiscatalyst, to convert at least a portion of the 2-pentene to 2-butene and3-hexene and recovering a second metathesis product; and a secondfractionation system for fractionating the second metathesis product torecover a 2-butene fraction and a 3-hexene fraction. The system may alsoinclude a flow conduit for diverting the second metathesis product tothe first fractionation system, providing system flexibility for theproduction of propylene only.

In another aspect, embodiments disclosed herein relate to a system forthe production of olefins. The system may include: anisomerization/metathesis reactor including an inlet for feeding a mixedC4-olefin stream comprising a mixture of 1-butene and 2-butene andincluding a first reaction zone comprising an isomerization catalyst anda second reaction zone comprising a first metathesis catalyst for:contacting the C4-olefin stream with the isomerization catalyst in thefirst reaction zone to form an isomerization product comprising 2-buteneand 1-butene; contacting the isomerization product with the metathesiscatalyst in the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene.The system may also include: a fractionation system for fractionatingthe first metathesis product to form an ethylene fraction, a propylenefraction, a C4 fraction and a C5+ fraction comprising 2-pentene and3-hexene; a metathesis reactor for contacting ethylene and the C5fraction with a second metathesis catalyst, which may be the same ordifferent than the first metathesis catalyst, to convert at least aportion of the ethylene and 2-pentene to propylene and 1-butene and toconvert at least a portion of the 3-hexene and ethylene to 1-butene andrecovering a second metathesis product; and a flow conduit for feedingthe second metathesis product to the fractionation system.

Other aspects and advantages will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified process flow diagram of a process for producinghigh purity 2-pentenes according to embodiments disclosed herein.

FIG. 2 is a simplified process flow diagram of anisomerization/metathesis reactor for use in processes for producing1-butene (and/or propylene) or 1-hexene according to embodimentsdisclosed herein.

FIG. 3 is a simplified process flow diagram of anisomerization/metathesis reactor for use in processes for producingbutenes according to embodiments disclosed herein.

FIG. 4 is a chart illustrating the changes in reactant and productequilibrium passing through an isomerization/metathesis reactoraccording to embodiments disclosed herein.

FIG. 5 is a simplified process flow diagram of a process for producinghigh purity 1-butene according to embodiments disclosed herein.

FIG. 6 is a simplified process flow diagram of a process for producinghigh purity 1-butene according to embodiments disclosed herein.

FIG. 6A is a simplified process flow diagram of a process for producingpropylene according to embodiments disclosed herein.

FIG. 7 is a simplified process flow diagram of a process for producinghigh purity 1-butene according to embodiments disclosed herein.

FIG. 8 is a simplified process flow diagram of a process for producinghigh purity 1-butene according to embodiments disclosed herein.

FIG. 9 is a plot illustrating 1-butene and n-butene conversion duringexperiments operating a process according to embodiments herein.

FIG. 10 is a plot illustrating product selectivity during experimentsoperating a process according to embodiments herein.

FIG. 11 is a plot illustrating 2-pentene to 1-pentene ratios duringexperiments operating a process according to embodiments herein.

DETAILED DESCRIPTION

In one aspect, embodiments herein relate to the production of highpurity alpha olefins, such as 1-butene and 1-hexene. More specifically,embodiments disclosed herein relate to the more efficient production andpurification of alpha-olefins utilizing isomerization and metathesis.

Processes disclosed herein utilize isomerization to favor the productionof a high purity beta-olefin, which is easily separable based on carbonnumber, and that may be used as a chemical intermediate for theproduction of a high purity alpha-olefin. Embodiments disclosed hereinthus eliminate the need of the butenes superfractionator, from 1-buteneand 1-hexene processes that, as noted in the Background above, is usedto produce a high-purity 1-butene stream from a mixed stream ofn-butenes.

The production of a high purity beta-pentene from 1-butene may beachieved in by isomerization and metathesis. The isomerization andmetathesis are performed in segregated reaction zones, in the same ordifferent reactors, thus limiting the isomerization and cross-metathesesof the desired intermediate.

For example, when contained in the same reactor, such as a downflowreactor, the segregated reactions may be performed with a catalyst bedconfiguration including an upper section to perform double-bondisomerization of n-butenes (1-butene and 2-butene) and a lower sectionto perform cross-metathesis between the formed 1-butene and 2-butene.This catalyst bed configuration allows for the use of any mixture ofn-butenes as feed to exclusively produce a high-purity 2-pentene (withessentially no 1-pentene) and propylene stream at high equilibriumproduct selectivities (>90%) with low levels of ethylene and hexeneformation.

The formed 2-pentene stream can be easily separated from co-productspropylene, ethylene and 3-hexene without the use of an extensiveseparation scheme, e.g., superfractionation. This high-purity 2-pentenestream attained may then be further processed to produce high puritystreams of 1-butene and 1-hexene.

Embodiments disclosed herein circumvent the need to separate the1-butene from its positional isomer (2-butene) by distillation in asuperfractionator. This is a major improvement for the current comonomerproduction processes, as it eliminates a highly energy intensive butenessuperfractionator from both 1-butene and 1-hexene production processes.This makes the processes to make 1-butene and 1-hexene economically moreattractive. Another advantage over the conventional 1-butene and1-hexene processes embodiments disclosed herein may allow olefin productflexibility, as producers can also withdraw propylene as a by-product,unlike the conventional CPT processes.

For the high purity 1-butene process according to embodiments herein,the exclusive 2-pentene (without 1-pentene) stream is further processedin a metathesis reactor and reacted via cross-metathesis with ethyleneto selectively form 1-butene and propylene, which can be easilyseparated and/or recycled.

For the high purity 1-hexene process according to embodiments herein,the exclusive 2-pentene (without 1-pentene) stream is further processedin a metathesis reactor and reacted via self-metathesis with itself toselectively form 3-hexene and 2-butene, which can be easily separatedand recycled to the original n-butenes feed stream. The formed 3-hexenemay then undergo further double-bond isomerization to produce a mixtureof linear hexenes, which may be fed to a hexenes superfractionationsystem to separate the 1-hexene product. However, in the overallprocess, the exclusive 2-pentene production of 1-butene and with itself(self-metathesis) can be easily separated through simple distillationand can be further used in various other process applications (highpurity polymer grade 1-butene production and 1-hexene production;isoprene production, etc). Thus, the process reduces the need for theenergy intensive separation by distillation of the alpha-olefin from itspositional isomers.

Segregated OCU for 2-Pentenes Production

Referring now to FIG. 1, processes according to embodiments herein mayproduce 2-pentenes via isomerization and metathesis using segregatedisomerization and metathesis reaction zones 6, 10, respectively, whichmay be in the same or different reactors. In some embodiments, thesegregated OCU (olefin conversion unit) is a reactor system 5 includingan upstream reaction zone 6 to perform double-bond isomerization ofn-butenes to form an equilibrium mixture 8 of 1-butene and 2-butenes,followed by a downstream reaction zone 10 to perform cross-metathesisbetween the formed 1-butene and 2-butene products from the reaction zone6. This segregated reaction zone configuration allows for the use of anymixture of n-butenes as feed 2 to exclusively produce a constanthigh-purity 2-pentene (i.e., without 1-pentene) and propylene productstream 12 at high product selectivities (>90%) and with littleby-products, i.e., ethylene and hexene. The formed 2-pentene stream 12can be easily separated from the product mixture without the use of anextensive separation scheme, e.g., superfractionation, such as in afractionation system 14, which may include a depropylenizer, separatingthe propylene product 16 from the 2-pentene product 28.

In some embodiments, the segregated OCU (olefin conversion unit) is asingle downflow reactor 5, such as illustrated in FIG. 2, where likenumerals represent like parts. Reactor 5 may include a catalyst bed 6 inthe upper portion of the reactor 5 to perform double-bond isomerizationof n-butenes to form an equilibrium mixture 8 of 1-butene and 2-butenes,followed by a catalyst bed 10 in the lower portion of the reactor 5 toperform cross-metathesis between the formed 1-butene and 2-buteneproducts from the upper reaction zone 6. This catalyst bed configurationallows for the use of any mixture of n-butenes as feed 2 to exclusivelyproduce a constant high-purity 2-pentene (without 1-pentene) andpropylene product stream 12 at high product selectivities (>90%) withlittle by-products, i.e., ethylene and hexene. The formed 2-pentenestream can be easily separated from the product mixture without the useof an extensive separation scheme, e.g., superfractionation, such as ina fractionation system 14 separating the propylene product 16 from the2-pentene product 28.

FIG. 3 and FIG. 4 collectively show a schematic representation of oneembodiment of the segregated OCU reactor. In this example the feed 2 isa pure 100% 1-butene feed. Catalyst zone 6 includes 4 times more MgOrelative to the WO₃/SiO₂ metathesis catalyst (MgO:WO₃/SiO₂=4) incatalyst zone 10. The upper segregated double-bond isomerization MgOcatalyst zone 6 ensures that a constant equilibrium n-butenes mixturemaintaining a 2-butene to 1-butene ratio near 4 (B2/B1=4, at 315° C.) isattained at the starting point of the metathesis catalyst bed 10,irrespective of the raw n-butenes feed composition (irrespective of thefeed B2/B1 ratio). The relatively higher partial pressure of 2-butenenear equilibrium (B2/B1=4 in this example) at the starting point of themetathesis catalyst bed 10 suppresses the unwanted self-metathesis sidereaction of the 1-butene to produce ethylene and hexene [B1+B1←→C2+C6]from occurring, which eventually further becomes self-extinguished dueto the limited availability of 1-butene as the 1-butene becomes consumedpredominantly via the cross-metathesis with 2-butene [B2+B1←ΘP2+C3], asthe self-metathesis reaction of 2-butene is non-productive[B2+B2←→B2+B2].

Embodiments herein thus provide an efficient process scheme to convertany mixed linear C4 olefin process streams (varying from pure 1-buteneto pure 2-butene) to exclusively produce high purity 2-pentene (without1-pentene) at near equilibrium compositions. The formed exclusive2-pentene (without 1-pentene) stream can be easily separated throughsimple distillation and can be further used in various other processapplications (high purity polymer grade 1-butene production and 1-hexeneproduction) as described in the following sections.

In some embodiments, the metathesis product from theisomerization/metathesis reactor may have a 2-pentene to 1-pentene ratioof greater than 100. In other embodiments, the metathesis product fromthe isomerization/metathesis reactor may have a 2-pentene to 1-penteneratio of greater than 150, 200, 250, or 300.

Process for Producing High Purity 1-Butene

Referring now to FIG. 5, a simplified process flow diagram for producinghigh purity 1-butene is illustrated, where like numerals represent likeparts. For the 1-butene process, as described above, an exclusive2-pentene (without 1-pentene) stream 12 is produced from any n-butenesfeed stream 2 via reaction in reaction zone 5.

To produce 1-butene, the 2-pentene product stream may be further reactedvia cross-metathesis with ethylene 18 in a metathesis reactor 24 toselectively form a product stream 26 including 1-butene and propylene.The metathesis product 26 may then be fed to a fractionation system 30to separate the propylene from the 1-butene.

In some embodiments, the propylene fraction 32 may be fed to ametathesis reactor, either a separate reactor system, or recycled toreaction zone 5 to produce additional 1-butene. In other embodiments,the propylene fraction 32, or a portion thereof, may be removed as aseparate product, depending on the product mixture needs of a specificplant.

In some embodiments, it may be desirable to limit the amount of branchedbutenes (isobutene) fed to the system. In such an embodiment, theprimary feed for this process may be an n-butenes stream free ofbranched C4 species, such as may be produced from a CD-DeiB™ unit (notshown), used for concurrent isomerization of 1-butene to 2-butene andfractionation of the 2-butene from isobutene (available from LummusTechnology Inc.).

In the upstream double-bond isomerization section of reaction zone 5,double-bond isomerization of the n-butenes (Reaction 1) is the onlyreaction that occurs, providing an equilibrium mixture of n-butenes atthe starting point of the downstream metathesis catalyst bed.1-Butene←→2-Butene  (Reaction 1)In the downstream metathesis section of the reaction zone 5, thefollowing reactions occur that produces 2-pentene.1-Butene+2-Butene←→2-Pentene+Propylene  (Reaction 2)1-Butene+1-Butene←→Ethylene+3-Hexene  (Reaction 3)1-Butene+Propylene←→2-Pentene+Ethylene  (Reaction 4)

The isomerization/metathesis reactor effluent is then fed to a primaryseparation train which may include a deethylenizer, depropylenizer, anddebutenizer. The separated 2-pentene (the primary intermediate for1-butene production) and 3-hexene mixture from the debutanizer bottomsstream is then fed to a metathesis-only reactor with ethylene to formthe 1-butene (target a-olefin) product. These reactions can be writtenas follows.2-Pentene+Ethylene←→1-Butene+Propylene  (Reaction 5)3-Hexene+Ethylene←→1-Butene+1-Butene  (Reaction 6)

The separated propylene may be recycled back along with the recycled C4stream to the isomerization/metathesis reaction zone or can be drawn asa separate product. Propylene is consumed via Reaction 4 in theisomerization/metathesis reaction zone to produce additional 2-pentenerequired downstream to ultimately produce the final 1-butene product.The propylene recycle/product split ratio may be used to control theextent of Reaction 4 and is an adjustable parameter that allowsadditional flexibility to the overall process for co-production ofpolymer grade propylene in addition to the co-monomer grade 1-butene.

The 1-butene formed from Reaction 5 and Reaction 6 in themetathesis-only reactor (reactor 30) product can now be easily separatedfrom the effluent stream via a secondary separation train that consistsof a depropylenizer and debutenizer. This separation train allows theseparation of the product 1-butene from the mixture of product propyleneand unreacted ethylene, 2-pentene, and 3-hexene feeds that may berecycled if desired (C3's and C4's to the isomerization/metathesisreaction zone, C2's to the metathesis-only reactor).

Ethylene is produced as a by-product from the isomerization/metathesisreaction zone from n-butenes as feed via Reactions 3 and 4 and is notrequired to be added as a separate feed source for this process scheme.However, optionally fresh ethylene may be added as feed to improve the1-butene product yields by adjusting the product selectivities in themetathesis-only reactor. One reason for maintaining excess ethylene inthe metathesis-only reactor would be to improve the 1-butene productpurity by reducing the only possible secondary nonselective reactionpathway that exists to form 2-butene in the metathesis-only reactor thatshould be avoided in the production of co-monomer grade 1-butene:Propylene+2-Pentene←→1-butene+2-butene  (Reaction 7)This is a secondary reaction that may occur between the propylene formedfrom Reaction 5 and 2-pentene that enters as feed in the metathesis-onlyreactor. Depending on the isobutene in the fresh n-butenes to theisomerization/metathesis reaction zone, purges are taken in the C4 andC5+C6 recycle streams to prevent isobutene, isopentene and isohexenesbuildup. These purge streams also allow to prevent buildup of any C4,C5, and/or C6 alkanes that have been introduced with the original mixedbutenes containing feed.

One embodiment for the overall process to produce high purity 1-butenemay be as illustrated in FIG. 6, where like numerals represent likeparts. As described above, feed butenes 2, which may be a mixture ofnormal butenes, pure 1-butene, or pure 2-butene, may be fed to reactionzone 5, including an isomerization zone 6 and a segregated metathesiszone 10, for producing an isomerization/metathesis product 12 including2-pentene and propylene, as well as some by-product ethylene and3-hexene.

The isomerization/metathesis product 12 may then be fed to afractionation system 14 for separation of the products, byproducts, andunreacted reactants (normal butenes). Fractionation system 14 mayinclude a deethylenizer 50, a depropylenizer 52, and a debutenizer 54.The deethylenizer may be used to separate an ethylene fraction 56 fromheavier hydrocarbons. The depropylenizer 52 may be used to recover apropylene fraction 16, a portion of which may be recovered as apropylene product 58. The debutenizer 54 may be used to separate a C4fraction 60 from a fraction 28, including 2-pentenes and any C6'sproduced.

Fresh ethylene 18, recycled ethylene 56, and 2-pentene fraction 28 maythen be fed to metathesis reaction zone 24. In metathesis reaction zone24, the 2-pentene may react with ethylene to produce 1-butene, and any3-hexene byproduct from the isomerization/metathesis reaction zone 5 maybe reacted with ethylene to additionally produce 1-butene. Effluent 26may thus include 1-butene (target product), propylene, as well asunreacted 2-pentene, 3-hexene, and ethylene.

The effluent 26 from metathesis reaction zone 24 may then be fed to afractionation zone 30, which may include a depropylenizer 70 and adebutenizer 72. The depropylenizer 70 may be used to separate a fraction32 including ethylene and propylene from a bottoms fraction 74.Debutenizer 72 may then be used to separate 1-butene from the unreacted2-pentene and 3-hexene, where the 1-butene may be recovered as anoverheads fraction 34 and the heavies may be recovered as a bottomsfraction 76.

The fraction 32 may be fed to separation system 14 for separation andrecovery of ethylene and propylene fractions 56, 16, as described above.Ethylene fraction 56 may be recycled to metathesis reactor 24. Propyleneand butene fractions 16 and 60 may be recycled toisomerization/metathesis reaction zone 5. Heavies fraction 76 may alsobe recycled to metathesis reactor 24 for continued conversion of the C5and C6 components. As necessary, a C4 purge may be taken via flow stream80 and a C5/C6 purge may be taken via flow stream 82.

In some embodiments, the process of FIG. 6 may be modified, with minoradjustments, to produce propylene as the sole product without any1-butene, such as illustrated in FIGS. 6 and 6A, where like numeralsrepresent like parts.

Referring now to FIG. 6A, as described above, feed butenes 2, which maybe a mixture of normal butenes, pure 1-butene, or pure 2-butene, may befed to reaction zone 5, including an isomerization zone 6 and asegregated metathesis zone 10, for producing an isomerization/metathesisproduct 12 including 2-pentene and propylene, as well as some by-productethylene and 3-hexene.

The isomerization/metathesis product 12 may then be fed to afractionation system 14 for separation of the products, byproducts, andunreacted reactants (normal butenes). Fractionation system 14 mayinclude a deethylenizer 50 and a depropylenizer 52. The deethylenizermay be used to separate an ethylene fraction 56 from heavierhydrocarbons. The depropylenizer 52 may be used to recover a propylenefraction 16, a portion or all of which may be recovered as a propyleneproduct 58, a C4 fraction 60, which may be recovered as a side draw, anda heavies fraction 28, including 2-pentenes and any C6's produced.

Fresh ethylene 18, as necessary, recycled ethylene 56, and heaviesfraction 28 may then be fed to metathesis reaction zone 24. Inmetathesis reaction zone 24, the 2-pentene may react with ethylene toproduce 1-butene, and any 3-hexene byproduct from theisomerization/metathesis reaction zone 5 may be reacted with ethylene toadditionally produce 1-butene. Effluent 26 may thus include 1-butene,propylene, as well as unreacted 2-pentene, 3-hexene, and ethylene.

The effluent 26 from metathesis reaction zone 24 may then be fed tofractionation system 14, as described above. The butenes produced inmetathesis reactor 24 are separated and recycled back to reaction zone 5to produce propylene. In such an embodiment, significant amounts ofpropylene may be formed from mixed butenes with little or no externallysupplied ethylene.

Referring back to FIG. 6, the process described above, producingpropylene 58 and high purity 1-butene stream 34, may be modified toprovide flexibility to produce propylene only, similar to that of FIG.6A, such as to meet added market demand for propylene or when demand forhigh purity 1-butene is low. In such instances, the second metathesisproduct 26 recovered from metathesis reactor 24 may be diverted tofractionation system 14 via flow line 29, and fractionation system 30may be taken off-line. When producing propylene as the primary product,a majority or all of propylene stream 16 may be recovered as product viaflow line 58. Suitable valving and control systems may also be includedto facilitate the desired process flexibility.

Process for Producing 1-Hexene

As described above with respect to the 1-butenes process, the 1-hexeneprocess according to embodiments herein begins with the initialproduction of an exclusive 2-pentene (without 1-pentene) stream, whichmay also include some 3-hexene from an n-butenes feed stream. The2-pentene is then further reacted via self-metathesis (autometathesis)in a metathesis reactor to selectively form 3-hexene. All formed3-hexene is separated and further isomerized in a double-bondisomerization-only reactor (reactor 3) to produce an equilibrium mixtureof hexenes (1-, 2-, and 3-hexenes). The 1-hexene product is then finallyseparated via a superfractionator.

Referring now to FIG. 7, a simplified process flow diagram of a processfor producing 1-hexene according to embodiments herein is illustrated,where like numerals represent like parts. Similar to the 1-buteneprocess, as described above, an exclusive 2-pentene (without 1-pentene)stream 12 is produced from any n-butenes feed stream 2 via reaction inreaction zone 5. A simple fractionation system 14 may then be used toseparate the propylene fraction 16 from the 2-pentene fraction 28

To produce 1-hexene, the 2-pentene product stream 28 may be furtherreacted via self-metathesis (autometathesis) in a metathesis reactor 90to selectively form a product stream 92 including 3-hexene and 2-butene.The metathesis product 92 may then be fed to a fractionation system 94to separate the 3-hexene 96 from the 1-butene 98.

Following separation, the 3-hexene fraction 96 may be fed to anisomerization reactor 100 for the double-bond isomerization of 3-hexeneto form an effluent 102 including positional isomers 1-hexene and2-hexene as well as unreacted 3-hexene. The effluent 102 may then beseparated in a fractionation system 104 to recover a 1-hexene fraction106 and a 2-hexene and 3-hexene fraction 108. In some embodiments, theeffluents from the isomerization/metathesis reaction zone 5 and themetathesis reaction zone 90 may be fed to a common fractionation system14/94, such as shown in FIG. 8.

The sole feed for this process is an n-butenes stream 2, which may befree of branched C4 species. The n-butenes feed stream may be fed to anisomerization/metathesis reaction zone including an upstreamisomerization reaction zone and a downstream reaction zone, producing aneffluent including target products 2-pentene and propylene, as well asbyproducts ethylene and 3-hexene as well as any unreacted n-butenes.

In the upstream double-bond isomerization reaction zone, double-bondisomerization of the n-butenes is the only reaction (Reaction 8) thatoccurs, and provides an equilibrium mixture of n-butenes at the startingpoint of the downstream metathesis reaction zone.1-Butene←→2-butene  (Reaction 8)In the downstream metathesis reaction zone 10, the following reactionsoccur that produces 2-pentene.1-Butene+2-Butene←→2-Pentene+Propylene  (Reaction 9)1-Butene+1-Butene←→Ethylene+3-Hexene  (Reaction 10)

The main by-products of ethylene and propylene form via Reactions 9 and10 and may be recovered from the isomerization/metathesis reactioneffluent in a fractionation system as separate product streams. Forexample, the separation train may include a deethylenizer, adepropylenizer, a debutenizer, and a depentenizer. The separated2-pentene stream may be fed to a metathesis-only reactor to form a3-hexene product via autometathesis. These reactions can be written asfollows.2-pentene+2-pentene←→3-hexene+2-butene  (Reaction 11)

The effluent stream from the metathesis reactor, containing 3-hexene,1-butene and unreacted 2-pentene, may then be re-routed and added to thedepropylenizer bottoms streams, which allows the 1-butene and 2-pentenestreams to be recycled and separate the 3-hexene to be further processeddownstream. All formed 3-hexene is separated from the depentenizerbottoms stream that is sent to a double-bond isomerization-only reactor.The 3-hexene is isomerized to produce an equilibrium mixture of hexenes(1-, 2-, and 3-hexenes) via reactions 12 and 13.3-Hexene←→2-Hexene  (Reaction 12)2-Hexene←→1-Hexene  (Reaction 13)

The 1-hexene product is then finally separated via a superfractionator.Depending on the isobutene in the fresh n-butenes fed to the unit,purges may be taken in each of the C4, C5, and C6 recycle streams toprevent isobutene, isopentene and isohexene buildup. These purge streamsalso allow to prevent buildup of any C4, C5, and/or C6 alkanes that havebeen introduced with the original mixed butenes containing feed.

One embodiment for the overall process to produce high purity 1-hexenemay be as illustrated in FIG. 8, where like numerals represent likeparts. As described above, feed butenes 2, which may be a mixture ofnormal butenes, pure 1-butene, or pure 2-butene, may be fed to reactionzone 5, including an isomerization zone 6 and a segregated metathesiszone 10, for producing an isomerization/metathesis product 12 including2-pentene and propylene, as well as some by-product ethylene and3-hexene.

The isomerization/metathesis product 12 may then be fed to a commonfractionation system 14/94 for separation of the products, byproducts,and unreacted reactants (normal butenes). Fractionation system 14 mayinclude a deethylenizer 50, a depropylenizer 52, a debutenizer 54, and adepentenizer 55. The deethylenizer 50 may be used to separate anethylene fraction 56 from heavier hydrocarbons. The depropylenizer 52may be used to recover a propylene fraction 16. The debutenizer 54 maybe used to separate a C4 fraction 60. The depentenizer 55 may be used toseparate a 2-pentene fraction 28, recovered as an overheads, from a3-hexene fraction 96, recovered as a side draw, and a C6+ purge 110,recovered as a bottoms fraction.

The 2-pentene fraction 28 may then be fed to metathesis reaction zone90. In metathesis reaction zone 90, the 2-pentene may react with itselfvia autometathesis to produce 2-butene and 3-hexene. Effluent 92 maythus include 3-hexene (target product), 2-butene, as well as unreacted2-pentene. The effluent 92 from metathesis reaction zone 90 may then befed to common fractionation zone 14/94, such as intermediate todebutenizer 54, for separation and recovery of the 3-hexene from thelighter components as described above.

Following separation, the 3-hexene fraction 96 may be fed to anisomerization reactor 100 for the double-bond isomerization of 3-hexeneto form an effluent 102 including positional isomers 1-hexene and2-hexene as well as unreacted 3-hexene. The effluent 102 may then beseparated in a superfractionation system 104 to recover a 1-hexenefraction 106 and a 2-hexene and 3-hexene fraction 108, which may berecycled to isomerization reactor 100 for additional conversion of the2- and 3-isomers to 1-hexene. As necessary, a C4 purge 112, a C5 purge114, and a C6 purge 116 may be withdrawn from the system.

In some embodiments, it may be desirable to recycle a portion ofpropylene stream 16 back to reaction zone 5, such as via stream 120. Therecycled propylene may react with the 1-butene present in the reactor toproduce additional 2-pentene within the reaction zones.

While described above with respect to production of high purity 1-butene(and/or propylene) or 1-hexene, other potential uses for the very highpurity 2-pentene stream may be considered. For example, the high purity2-pentene stream produced from a segregated olefins conversion unitusing n-butenes as feed could also be used to produce isoprene, such asvia a 2-methyl-2-pentene intermediate formed from 2-pentene reacted withisobutene, described in US 2011/0034747, which is incorporated herein byreference in its entirety.

As described above, processes for the production of olefins according toembodiments herein may include: contacting a hydrocarbon mixturecomprising linear butenes with an isomerization catalyst to form anisomerization product comprising 2-butenes and 1-butenes; contacting theisomerization product with a first metathesis catalyst to form a firstmetathesis product comprising 2-pentene and propylene, as well as anyunreacted C₄ olefins, and byproducts ethylene and 3-hexene;fractionating the first metathesis product to form a C3− fraction and aC5+ fraction comprising 2-pentene, which may be a high purity 2-pentenefraction.

For the production high purity 1-butene, the process may also includecontacting ethylene and the C5+ fraction with a second metathesiscatalyst, which may be the same or different than the first metathesiscatalyst, to convert at least a portion of the 2-pentene and ethylene topropylene and 1-butene and form a second metathesis product. The secondmetathesis product may then be readily fractionated to recover apropylene fraction and a high purity 1-butene fraction. In someembodiments, the 1-butene fraction may have a purity of at least 98 wt %1-butene. In other embodiments, the 1-butene fraction may have a purityof at least 98.5 wt %, at least 99 wt %, or at least 99.5 wt % 1-butene.

For the production of high purity 1-hexene, the process may also includecontacting the C5+ fraction with a second metathesis catalyst, which maybe the same or different than the first metathesis catalyst, to convertat least a portion of the 2-pentene to 2-butene and 3-hexene and form asecond metathesis product. The second metathesis product may then bereadily fractionated to recover a 2-butene fraction and a 3-hexenefraction. The 3-hexene fraction has a purity of at least 98 wt %3-hexene. In some embodiments, the 3-hexene fraction may have a purityof at least 98 wt % 3-hexene. In other embodiments, the 3-hexenefraction may have a purity of at least 98.5 wt %, at least 99 wt %, orat least 99.5 wt % 3-hexene. The 3-hexene may then be converted viaisomerization to 1-hexene.

In embodiments disclosed herein, the isomerization/metathesis reactor 5,6, 10, and/or the metathesis reactors 24, 90 may be operated at apressure between 2 and 40 atmospheres, and between 5 and 15 atmospheresin other embodiments. The reactors may be operated such that thereaction temperature is within the range from about 50° C. to about 600°C.; within the range from about 200° C. to about 450° C. in otherembodiments; and from about 250° C. to about 400° C. in yet otherembodiments. The isomerization and metathesis reactions may be performedat a weight hourly space velocity (WHSV) in the range from about 2 toabout 200 in some embodiments, and from about 6 to about 40 in otherembodiments.

The reactions may be carried out by contacting the olefin(s) with theisomerization and/or metathesis catalysts in the liquid phase or the gasphase, depending on structure and molecular weight of the olefin(s). Ifthe reaction is carried out in the liquid phase, solvents or diluentsfor the reaction can be used. Aliphatic saturated hydrocarbons, e.g.,pentanes, hexanes, cyclohexanes, dodecanes and aromatic hydrocarbonssuch as benzene and toluene are suitable. If the reaction is carried outin the gaseous phase, diluents such as saturated aliphatic hydrocarbons,for example, methane, ethane, propane, normal and branched C4, C5,alkanes and/or substantially inert gases, such as nitrogen and argon,may be present. For high product yield, the reactions may be conductedin the absence of significant amounts of deactivating materials such aswater and oxygen.

The contact time needed to obtain a desirable yield of reaction productsdepends upon several factors such as the activity of the catalyst,temperature, pressure, and the structure of the olefin(s) to beisomerized and/or metathesized. Length of time during which theolefin(s) are contacted with catalyst can vary between 0.1 seconds and 4hours, preferably from about 0.5 sec to about 0.5 hrs. The isomerizationand metathesis reactions may be conducted batch-wise or continuouslywith fixed catalyst beds, slurried catalyst, fluidized beds, or by usingany other conventional contacting techniques.

The catalyst contained within the metathesis reactor may be any knownmetathesis catalyst, including oxides of Group VIA and Group VITA metalson supports. Catalyst supports can be of any type and could includealumina, silica, mixtures thereof, zirconia, magnesia, titania, andzeolites. In some embodiments, the metathesis catalyst is tungsten oxideon silica.

The double bond isomerization catalyst may be any known double bondisomerization catalyst. In some embodiments, the double bondisomerization catalyst may be one of magnesium oxide, calcium oxide,aluminum oxide, or mixed Mg—Al oxides (e.g, hydrotalcite-derived mixedoxides), among other possible catalysts.

In some embodiments, the double bond isomerization catalyst may be analumina-titania catalyst. The catalyst may be a γ-alumina-titaniacrystalline mixture including active sites that catalyze the positionalisomerization of olefins, and may be in the form of pellets, extrudates,and the like, and will typically have an effective diameter of 0.5 mm to5 mm, such as in the range from 1 mm to 4 mm, or in the range from 2 mmto 3 mm. In some embodiments, the alumina-titania catalyst may have acomposition of titanium with a lower limit of 0.01, 1, 2, 3, 4, 5, 10,15, 20, or 25 to an upper limit of 15, 20, 25, 30, 35, 40, 45, or 50 wt%, where any lower limit may be combined with any upper limit.γ-Alumina-titania catalyst herein may have a surface area in someembodiments greater than 200 m²/g, in other embodiments greater than 250m²/g, in other embodiments greater than 300 m²/g, in other embodimentsgreater than 350 m²/g, and in other embodiments greater than 400 m²/g.The γ-alumina-titania catalysts may be tolerant of oxygenated speciesthat are typically considered a poison, such as to MgO type catalysts,may act as an oxygenate scavenger protecting downstream catalyst beds,and in some embodiments may have activity for dehydration of alcohols inaddition to isomerization activity. The γ-alumina-titania catalysts mayalso be more forgiving with respect to cyclopentene purity of the feed,and may allow greater than 5 wt %, greater than 7.5 wt %, or evengreater than 10 wt % cyclopentene to be present in the feed, potentiallynegating typical upstream processes required to remove cyclopentene fromthe feed. These γ-alumina-titania catalysts may be used alone, such asin an isomerization only reactor or in an isomerization catalyst bed ina segregated OCU, or may be used in admixture with other isomerizationcatalysts or metathesis catalysts.

EXAMPLES

Production of high purity 2-pentene, such as by the process as shown inFIG. 1, was performed. Testing results from the laboratory-scale testsare provided in FIGS. 9-11. This test was performed in a reactor loadedin a “segregated OCU” reactor configuration with an upper catalyst bedof MgO for double-bond isomerization-only and a lower catalyst bed forexclusive metathesis activity using a pure 1-butene stream as feed. Four(4) times more MgO catalyst was loaded relative to the metathesiscatalyst load to ensure a constant equilibrium n-butenes mixturemaintaining a 2-butene to 1-butene ratio of 4 (B2/B1=4) is attained atthe starting point of the WO₃/SiO₂ catalyst bed. As shown in FIG. 9,very high once through 1-butene conversion levels (>97%) were achievedand maintained 50 hours time-on-stream (TOS). Excellent stableequilibrium product selectivities towards desired products (2-pentenesand propylene) near 95% were achieved at 316° C. (600° F.) and 120 psigas shown in FIG. 10. The 2-pentenes to 1-pentene (P2/P1) ratios of theproduct stream exhibited a somewhat broad range between 130-285 as shownin FIG. 11.

This data clearly indicates that the pentenes product produced via thesegregated OCU reactor configuration produces an almost exclusivemixture of 2-pentenes with very low levels of 1-pentene being formed.The relatively high variability observed in the P2/P1 ratios is mostlydue to relatively high errors in GC (gas chromatogram) peak integrationsof the very small amounts of 1-pentene present. Furthermore, the resultsshown here are provided for demonstration of the concept and not fullyoptimized. Thus, the purity of the 2-pentenes product can besignificantly improved from those provided in this example and shown inFIGS. 9-11.

The upper and lower catalyst sections can be either located in a singlereactor or two (2) separate reactors in series. For the case of twoseparate reactors, the first reactor is used to only perform double-bondisomerization, and the second reactor is used exclusively for metathesisof the effluent product stream from the first reactor. Furthermore, eachreactor may be operated as a completely separate reactor and thusallowing to operate under different reaction conditions (e.g, differenttemperatures, pressures, and different WHSV (weighted hourly spacevelocities) to maximize the yield of product or to reduce overalloperational costs.

As described above, embodiments disclosed herein provide for theproduction of a high purity 2-pentene stream. The high purity 2-pentenestream may then be advantageously used to produce end products such asisoprene, high purity 1-butene, and high purity 1-hexene.

While the disclosure includes a limited number of embodiments, thoseskilled in the art, having benefit of this disclosure, will appreciatethat other embodiments may be devised which do not depart from the scopeof the present disclosure. Accordingly, the scope should be limited onlyby the attached claims.

What is claimed:
 1. A process for the production of olefins, the processcomprising: (a) contacting a hydrocarbon mixture comprising linearbutenes with an isomerization catalyst to form an isomerization productcomprising 2-butenes and 1-butenes; (b) contacting the isomerizationproduct with a first metathesis catalyst to form a first metathesisproduct comprising 2-pentene and propylene, as well as any unreactedbutenes, and byproducts ethylene and 3-hexene; (c) fractionating thefirst metathesis product to form a C3− fraction comprising propylene andethylene and a C5 fraction comprising 2-pentene; and recycling the C3−fraction to step (a) or step (b).
 2. The process of claim 1, furthercomprising (d) contacting ethylene and the C5 fraction with a secondmetathesis catalyst, which may be the same or different than the firstmetathesis catalyst, to convert at least a portion of the 2-pentene andethylene to propylene and 1-butene and form a second metathesis productcomprising propylene and 1-butene.
 3. The process of claim 2, furthercomprising (e) fractionating the second metathesis product to form apropylene fraction and a 1-butene fraction.
 4. The process of claim 3,further comprising recycling the propylene fraction to at least one ofstep (a) and step (b).
 5. The process of claim 3, wherein the 1-butenefraction has a purity of at least 98 wt % 1-butene.
 6. The process ofclaim 1, further comprising (d) contacting the C5 fraction with a secondmetathesis catalyst, which may be the same or different than the firstmetathesis catalyst, to convert at least a portion of the 2-pentene to2-butene and 3-hexene and form a second metathesis product comprising2-butene and 3-hexene.
 7. The process of claim 6, further comprising (e)fractionating the second metathesis product to form a 2-butene fractionand a 3-hexene fraction.
 8. The process of claim 7, further comprisingrecycling the 2-butene fraction to step (a).
 9. The process of claim 6,wherein the 3-hexene fraction has a purity of at least 98 wt % 3-hexene.10. The process of claim 8, further comprising converting the 3-hexenefraction via isomerization to 1-hexene.
 11. The process of claim 1,further comprising converting the 2-pentene in the C5 fraction toisoprene.
 12. The process of claim 1, wherein the first metathesisproduct has a 2-pentene to 1-pentene ratio of greater than
 100. 13. Aprocess for the production of olefins, the process comprising: feedingpropylene and a mixed C4-olefin stream comprising a mixture of 1-buteneand 2-butene to an isomerization/metathesis reactor including a firstreaction zone comprising an isomerization catalyst and a second reactionzone comprising a first metathesis catalyst; contacting the propyleneand mixed C4-olefin stream with the isomerization catalyst in the firstreaction zone to form an isomerization product comprising 2-butene and1-butene; contacting the isomerization product with the first metathesiscatalyst in the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene;feeding the first metathesis product to a fractionation system;fractionating the first metathesis product in the fractionation systemto form at least one C3− fraction comprising propylene and ethylene anda C5 fraction comprising 2-pentene.
 14. A process for the production ofolefins, the process comprising: feeding a mixed C4-olefin streamcomprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the mixed C4-olefinstream with the isomerization catalyst in the first reaction zone toform an isomerization product comprising 2-butene and 1-butene;contacting the isomerization product with the first metathesis catalystin the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene;feeding the first metathesis product to a fractionation system;fractionating the first metathesis product in the fractionation systemto form at least one C3− fraction comprising propylene and ethylene anda C5 fraction comprising 2-pentene; feeding ethylene and the C5 fractionto a metathesis reactor and contacting the ethylene and C5 fraction witha second metathesis catalyst, which may be the same or different thanthe first metathesis catalyst, to convert at least a portion of theethylene and 2-pentene to propylene and 1-butene and recovering a secondmetathesis product comprising propylene and 1-butene; fractionating thesecond metathesis product to recover a propylene fraction and a 1-butenefraction; and feeding at least a portion of the propylene fraction tothe isomerization/metathesis reactor.
 15. A process for the productionof olefins, the process comprising: feeding a mixed C4-olefin streamcomprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the mixed C4-olefinstream with the isomerization catalyst in the first reaction zone toform an isomerization product comprising 2-butene and 1-butene;contacting the isomerization product with the first metathesis catalystin the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene;feeding the first metathesis product to a fractionation system;fractionating the first metathesis product in the fractionation systemto form at least one C3− fraction comprising propylene and ethylene anda C5 fraction comprising 2-pentene; recycling the C3− fraction to theisomerization/metathesis reactor; feeding the C5 fraction to ametathesis reactor and contacting, in the absence of ethylene, the C5fraction with a second metathesis catalyst, which may be the same ordifferent than the first metathesis catalyst, to convert at least aportion of the 2-pentene to 2-butene and 3-hexane and recovering asecond metathesis product comprising 2-butene and 3-hexene; andfractionating the second metathesis product to recover a 2-butenefraction and a 3-hexene fraction.
 16. A process for the production ofolefins, the process comprising: feeding a mixed C4-olefin streamcomprising a mixture of 1-butene and 2-butene to anisomerization/metathesis reactor including a first reaction zonecomprising an isomerization catalyst and a second reaction zonecomprising a first metathesis catalyst; contacting the mixed C4-olefinstream with the isomerization catalyst in the first reaction zone toform an isomerization product comprising 2-butene and 1-butene;contacting the isomerization product with the first metathesis catalystin the second reaction zone to form a first metathesis productcomprising 2-pentene, propylene, and byproducts ethylene and 3-hexene;feeding the first metathesis product to a fractionation system;fractionating the first metathesis product in the fractionation systemto form an ethylene fraction, a propylene fraction, a C4 fraction and aC5+ fraction comprising 2-pentene and 3-hexene; feeding ethylene and theC5+ fraction to a metathesis reactor and contacting the ethylene and C5+fraction with a second metathesis catalyst, which may be the same ordifferent than the first metathesis catalyst, to convert at least aportion of the ethylene and 2-pentene to propylene and 1-butene and toconvert at least a portion of the 3-hexene and ethylene to 1-butene andrecovering a second metathesis product comprising propylene and1-butene; feeding the second metathesis product to the fractionationsystem; and feeding the propylene fraction to theisomerization/metathesis reactor.
 17. The process of claim 16, whereinthe ethylene fed to the metathesis reactor comprises at least a portionof the ethylene fraction.
 18. The process of claim 16, furthercomprising recycling at least a portion of the C4 fraction to theisomerization/metathesis reactor.
 19. The process of claim 16, whereinthe C4 fraction is recovered as a side draw from a depropylenizercolumn.